diff --git a/fs/dax.c b/fs/dax.c
index c576f6181dc8958951669fd6f91d2d18177874c7..5b2eac3ef077db86c8e916abae92e14d084eefd1 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1004,6 +1004,11 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		if (map_len > end - pos)
 			map_len = end - pos;
 
+		/*
+		 * The userspace address for the memory copy has already been
+		 * validated via access_ok() in either vfs_read() or
+		 * vfs_write(), depending on which operation we are doing.
+		 */
 		if (iov_iter_rw(iter) == WRITE)
 			map_len = dax_copy_from_iter(dax_dev, pgoff, kaddr,
 					map_len, iter);